In recent years, the domestic energy sector has changed to a free market economy in a number of states and countries in the U.S. and Europe. This offers unprecedented opportunities for innovation, in bringing the utility sector up to par with modern technology, telecommunication and global commerce. We expect to witness novel competitive strategies in commercial metering, distribution and trading of electricity, natural gas and, possibly, water. This advance will be facilitated with the introduction of micro-electronic technology in metering of the consumption of natural gas.
Electronic metering of natural gas consumption is key to advanced home energy management systems. On the basis of real-time continuous measurements detailed insight can be gained in the relationship between gas consumption and a home climate, as well as the operation of home appliances. These data can further be used to perform detailed analysis of home energy saving measures, such as the installation of highly-efficient central heating sys-tems and insulating double-glass windows. To this end, we here propose a desktop display of domestic consumption of natural gas. Such will be possible by wireless interfacing to a fully electronic gas meter. This development is particularly interesting, in view of recent raises and uncertainties in the price and availability of natural gas, both in the US and Europe.
At present, metering of natural gas is performed by mechanical metering devices. This hampers the process of bringing data “inside” (in the US) or “out of the closet” (in Europe) to the desktop. The larger goal is integration into a utility sensor network, facilitated by the internet or wireless telemetry system. A common “work-around” uses electronic readers attached to and on top of existing mechanical devices. An example of this approach can be found in a recent Automatic Meter Reading system of the Water Department of the City of Cambridge of Massachusetts. The disparity between mechanical sensing and electronic data transfer has long been recognized, and has led to a variety of initiatives to develop comptable meters which are fully electronic. However, these initiatives have as yet to produce commercially viable alternatives to existing mechanical meters.
Up to this day, the world-wide standard for metering domestic use of natural gas is the mechanical bellow-meter. By principle of operation, this device measures displacement of volume of natural gas. This introduces inevitably an uncertainty in the caloric content of gas used, as determined by the displacement of mass of natural gas. For example, systemic discrepancies in temperatures at purchase of natural gas by a gas distributor and at supply to a consumer introduces a systemic discrepancy in the expected caloric content paid for by the latter. The bellow-meters hereby do not guarantee “pay for what they get” in true heat, unless these devices are temperature compensated. (The pressure in domestic gas connections is kept constant to within high precision.) In view of the additional cost, temperature compensation is generally applied only in the metering of large-volume customers, e.g., office buildings, industry and agriculture. In this case, more advanced meters of rotary-type (e.g. ROOTS in the US or INSTROMET in Europe) or vortex-type are commonly used.
In this disclosure, we focus on a method for comptable metering of natural gas for domestic customers by thermal anemometry. Thermal anemometry is in principle and ideal measurement principle, in that it accurately measures mass-flow under a wide range of medium pressures. However, practical realizations have proven to be challenging in view of drift in response to temperature changes of the medium and the device, wherein the latter may have a variety of time-constants. This calls for a systematic approach for the design of a drift-free meter. For commercial applications, the cost of the manufacturing should be kept low by circumventing the need for detailed calibration procedures. For ease-of-use, the data must be communicated to the outside world by wireless interfacing. These data can then be presented to the desktop of the consumer for detailed analysis as input to energy-saving strategies. The same data can be offered to metering companies and the gas distributor for billing purposes and large-scale consumer analysis.
For comptable metering of natural gas, we shall work with the following basic requirements:
The output is caloric content by measuring mass-displacement of natural gas.
The flow-range covers 1 l/min to a few hundred l/min with pressure drop of a few mbar.
The device uses a single sensor and the response curve is drift free (with zero offset and zero multiplicative drift).
The objective of is to fix the response curve by geometry alone to circumvent detailed calibration procedures.
A brief description of the method is disclosed below, together with experimental results on the measurement of Reynolds number and temperature of air flow on the basis of a first-principle flow-generator, a preferred embodiment and a set of claims.